Picorna and Caliciviruses

October 14, 2009

Viruses with +ve RNA genomes

Picornaviridae

Caliciviridae

Coronaviridae

Arteriviridae

Flaviviridae

Togaviridae

feline calicivirus

equine arterivirus

pestiviruses (BVD)

coronaviruses

equine encephalitis viruses

EnteroAphtho

Rhino

HepatoCardio

Picornaviruses

• “pico” - small

• “rna” - RNA

• single stranded, positive RNA

• unenveloped, relatively stable

a hundred days of foot and mouth

BBC

Foot and mouth disease

• highly contagious disease of domestic and wild ruminants and pigs.

• systemic disease with high fever, vesicles on epithelial surfaces

• not usually fatal in adults but causes economic losses (trade implications)

• can be fatal in young animals - myocarditis

Susceptibility to inactivation

• pH– stable between pH 7 and 9– inactivated by:

• 5% acetic acid or other acids• 1-2% sodium hydroxide or other alkalis

• phenolic and quarternary ammonium compounds - not effective• oxidizing agents (bleach) effective when environment not

contaminated with organic substances. Detergents increase effectiveness

• heat– in suspension 80o for 1 hr, 50o for 2 days, 37o for seven days– stable when associated with dried organic matter (see Dekker,

1998, Vet. Rec 143:168)

CFIA recommendations for inactivation

• 50% solution of vinegar in water - 30 min

• sodium carbonate, 100 gm/L - 30 min

• citric acid powder - 2 gm/L - 30 min

Serotypes

• 7 serotypes - O, A, C, South African territories (SAT)-1, SAT-2, SAT-3, Asia

• At least 60 subtypes

from:Grubman and Baxt, 2004

Susceptible species• domestic ruminants (cattle, buffalo, sheep,

goats, camelids*)

• wild or exotic ruminants (african buffalo, various antelope and deer species)

• others (pigs, rabbits, mice, guinea pigs, chickens, elephants, humans)

• horses are resistant

Different effects on susceptible species

• pigs (amplifying hosts) - secrete large amounts of virus in breath, air borne spread

• cattle (sentinel hosts) - highly sensitive to infection by respiratory route

• sheep (maintenance hosts) - mild-asymptomatic disease, can spread through flocks before detection

Pathogenesisinfection(inhalation,ingestion,AI)

incubation period(1-21 days, usually 3-5 in cattle, 4-9 in pigs)

clinical signs(variable)

recovery(most animals but effects can persist)

persistence(months to years in partially immune animals, life time in some species)

virus shedding(begins 1-4 days beforeclinical signs appear)

death(myocarditis in young animals)

infectious dose = < 10 particles

Clinical signs

•fluid filled vesicles - on mucosa and face, feet, hairless areas - rupture to form ulcers

lameness - ulcers on feet

high fever - 40-41o

salivation, anorexia - lesions in mouth

Infection of heart muscle

young animals (up to 6 months of age in cattle)

Epidemiology• Factors that allow rapid spread and persistence in a population

– antigenic variation (7 serotypes with no cross protection and many antigenic variants with limited cross reactivity)

– large host-range (including wild-life)– low infectious dose (<10 particles)– large amounts of virus before clinical signs develop– no clinical signs in some species (sheep, cattle) allows

spread– persistent infection in partially immune animals– hardy virus (many routes of spread, airborne)

Prevention

• In countries with endemic FMD– vaccination

– vaccination and slaughter

• FMD free countries– prevent introduction

– in face of outbreak• test and slaughter

• ring-vaccination and slaughter

• ring-vaccination and slaughter only sick animals

Problems with vaccination• no cross protection if wrong serotype• short-lived immunity• partial protection if variant

– does not prevent infection– persistent infection

• cannot distinguish between vaccinated and infected animals

• detection easier if no vaccination

Regaining FMD-free status

• “stamping out” without vaccination - 3 months after last case

• slaughter and ring vaccination - 3 months after last slaughter of last vaccinated animal

• if all vaccinated animals are not slaughtered - – FMD free status with vaccination

• 12 months after last case

– to regain FMD free without vaccination• no cases for 12 months after last vaccination• no importation of vaccinated animals

• Techniques that distinguish between vaccinated and infected animals

New Developments

Diagnosis

• clinical signs - can be confused with other vesicular diseases

• laboratory– sample collection

• vesicle fluid, skin at edge of ruptured vesicle, excretions and secretions

• inoculated onto susceptible cells• if cpe - confirm FMD and serotype by capture ELISA• if no cpe - 2 “blind” passages

– PCR

Idiopathic vesicular disease in swine in ManitobaTim Pasma, Suzanne Davidson, Sheryl Shaw, 2008, CVJ

49:84-85

Tim Pasma, 2008, CVJ 49:84-85

Some viruses that cause vesicular disease in swine

• Foot and mouth disease (reportable)

• Swine vesicular disease (reportable)

• Vesicular stomatitis (reportable)

• Vesicular exanthema (not in N America)

• Porcine parvovirus

• Porcine enterovirus

Calicivirus

Caliciviruses

• vesicular exanthema of swine

• San Miguel sea lion virus

• feline calicivirus

• rabbit haemorrhagic virus

• bovine and porcine enteric caliciviruses

• chicken calicivirus

feline calicivirus

Fe calicivirus in exotic cats